AbstractSoil compaction occurs when soil particles are pressed together, thus reducing pore spaces between them. Compaction is caused by the use of heavy machinery, pressure from wheels, tillage equipment, trampling by animals reduced use of organic matter, frequent use of chemical fertilizers and ploughing at the same depth for many years. The signs of soil: Slow plant emergence, thin stands, uneven early growth, small grain heads, abnormal rooting patterns and reduced nutrients offtake can be a reflection of compation. Excessive soil compaction impedes root growth and therefore limits the amount of soil explored by roots. Soil compaction is a problem of global concern and very few have worked on this issue in Pakistan. Therefore this research work was conducted to investigate and document the deleterious effects of subsurface soil compaction on crop and soil properties, as well as to evaluate best and cheap improvement measures for reducing subsurface soil compaction

Two field experiments were conducted during the year 2002-03 and repeated during the year 2003-04 at the Agriculture Research Station, Mingora, Pakistan. In first experiment the effects of subsurface soil compaction were studied. In second experiment the effects of improvement measures applied to the artificially compated subsurface soil were investigated. In first experiment, the 0.1m surface horizon was removed from all the plots with the help of scraper. The subsurface was compated using 7.0 tons roller. The number of passes of roller measured the level of compation. The experiment consisted of four treatments. The subsurface soil was compacted with two passes of roller in T1, four passes of roller in T2 and six passes of roller in T3, while no compaction was applied to T4 (control). The topsoil was evenly applied to the whole plot and wheat variety Fakhri Sarhad was grown. In second experiment, the 0.1 meter surface soil was removed with a scrper. Different improvement measures were applied to subplots according to sowing plan. The experiment consisted of five treatments. T1 received deep ploughing (D.P), T2 received D.P+FYM at 14000kg/ja, T3 received D.P+Gypsum at 4000kg/ha, T4 received D.P +FYM+Gypsum at the rates mentioned above while T5 (control) no addition of improvement measure was made. The subsurface of the whole plot was then compacted with 4 passes of a 7.0 tons roller. The 0.1m surface soil was uniformly distributed in the plot with blade mounted tractor and scraper. Lay out was again carried out and deep ploughing was given to all the sub plots with chisel plough to a depth of 20cm except control. Wheat variety Fakhri Sarhad was frown in all the plots with a seeding rate of 140kg/ha-1

In first experiment compaction of the subsurface significantly affected days to anthesis, days to maturity, plant height spikes m-2, grains per spike, thousand grain weight, biological yield, grain yield, harvest index, crop growth rate (CGR), root length, subsurface soil bulk density, subsurface soil porosity, percent grain protein, N concentration in plants (%) and K concentration in plants (%), while non significant variations were observed for days to emergence, emergence per m2, tillers per m2, upper surface soil bulk density, upper surface soil porosity, total soil nitrogen, available soil phosphorous and available soil potash among different treatment means averaged over the years. The maximum values of above parameters were recorded to T4 (control) and the minimum for T3 except subsurface soil bulk density where the maximum values were recorded for T3 and the minimum for T4 (control). Almost all parameters showed a decreasing trend with increasing the level of subsurface soil compaction. Interactive effects varied inconsistently. Significant effects on different parameters may be attributed to changed physical conditions of the soil duw to compaction which ultimately affected growth and development parameters. However, slightly higher values were observed during second year of experiment as compared to first year which may be the effect of overall climatic conditions as during second year more rains were received. Average maximum and average minimum temperature was noticed to be lower than that recorded during first year which thus increased the total length of crop life cycle.

The maximum values of these parameters were recorded for T4 (D.P. +FYM+Gypsum) followed by T2 (D.P.+FYM), while minimum values were recorded for T5 (control), except subsurface soil bulk density where minimum values were recorded for T4 and T2 and maximum for T5 (control). The maximum values recorded for treatments where deep loughing + farm yard manure was added may be attributed that these amendments left positive effects on overall soil structure thus giving positive response. So, where soil compaction hinders in good crop production these amendments amy ameliorate the negative effects

Interactive effects varied inconsistently. However, slightly higher values were observed during second year of experiment as compared to first year